The present invention is directed to control devices for bicycles and, more particularly, to a twist-grip shifting device for shifting a bicycle transmission.
Twist-grip shifting devices that can rotate around their axes near handlebar ends and that extend in the longitudinal directions of the handlebar ends are used to manipulate takeup members in order to take up or pay out a shift control cable. After a takeup operation has been performed in such a manner, the takeup member must be positioned so that its location corresponds to the selected speed step. Known examples of positioning the takeup member include those merely involving the use of frictional resistance; those in which indentations are formed in the speed-step positions on the side of the fixed elements for engaging protrusions formed on the side of the control members (as described in Japanese Laid-Open Patent Application 3-176290); and those involving the provision of one-way ratchet mechanisms (as described in PCT/JP92/00138).
In twist-grip shifting devices where positioning is accomplished using frictional resistance or engagement between indentations and protrusions, considerable engagement force is needed to securely position the takeup member in the position corresponding to the selected speed step. This, in turn, results in a twist-grip shifting device in which considerable force is needed to implement the control operations. With twist-grip shifting devices in which positioning is accomplished using ratchet mechanisms, many components are required to construct the ratchet mechanisms, thus dramatically increasing the cost of the device.